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Use the definition of the derivative and factoring formulas to prove that for any positive integer k, the derivative ofxkis kxk-1

Short Answer

Expert verified

ddxxk=kxk-1

Step by step solution

01

Step 1:Given information

The given expresiion isfx=xk

02

Step 2:Explanation

We’ll need to restrict kto be a positive integer. In this case if we define fx=xk,

we know from the alternate limit form of the definition of the derivative that the derivative f'ais given by

f'a=limx→afx-fax-a=xk-xax-a

Now,

xk-xa=x-axk-1+axk-2+...ak-2x+ak-1

If we put this into the formula for the derivative we see that we can cancel the x-aand then compute the limit.

f'a=limx→ax-axk-1+axk-2+...ak-2x+ak-1x-a

⇒f'(a)=limx→axk-1+axk-2+...ak-2x+ak-1

⇒f'a=kak-1

To completely finish this off we simply replace the awith an xto get,

⇒f'x=kxk-1

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